Differential regulation of liver-specific and ubiquitously-expressed genes in primary rat hepatocytes by the extracellular matrix.

Primary rat hepatocytes were cultured with an extracellular matrix (ECM) overlay, in order to investigate the effect of an ECM on gene expression in hepatocytes. When hepatocytes, isolated by the collagenase-perfusion method, were cultured on type I collagen-coated dishes, the mRNA levels of liver-specific genes (aldolase B, tyrosine aminotransferase and albumin) decreased continuously, while those of ubiquitously-expressed genes (glyceraldehyde 3-phosphate dehydrogenase and beta-actin) increased. When a dilute ECM derived from the Engelbreth-Holm-Swarm mouse sarcoma (an EHS gel) was added to the above hepatocytes 3 days after plating, the mRNA levels of liver-specific genes increased, while those of ubiquitously-expressed genes decreased. The effects of a rat liver biomatrix (a physiological ECM for rat hepatocytes) on gene expression in primary hepatocytes were similar to those of the EHS gel. A nuclear run-on assay, and 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole or actinomycin D treatments revealed that the transcriptional rates of liver-specific genes were enhanced by the EHS gel overlay, while the apparent stability of the corresponding mRNAs were unchanged. In contrast, the transcriptional rates of ubiquitously-expressed genes were not greatly affected by an EHS gel overlay, while the apparent stability of their mRNAs were decreased. These data suggest that the ECM plays an important role in the maintenance of the differentiated characteristics of primary hepatocytes by inducing the transcription of liver-specific genes and, also, by destabilizing the mRNAs of ubiquitously-expressed genes.